Instrument shaft for computer-assisted surgical system

ABSTRACT

A shaft for a surgical instrument comprises an outer tube having a proximal end and a distal end, a central lumen extending through the outer tube, and a plurality of stiffening rods positioned around the central lumen. The plurality of stiffening rods may comprise a nonconductive material. The shaft may form part of an electrosurgical instrument. In another embodiment, a surgical instrument may comprise an end effector and a shaft having an outer tube having a proximal end and a distal end, a drive rod, and at least four stiffening rods positioned around the drive rod, each stiffening rod being positioned substantially immediately adjacent to the drive rod. The axial stiffness of the shaft increases incrementally during actuation of the end effector.

This application is a continuation of U.S. patent application Ser. No.14/911,977, filed Dec. 2, 2016, which is a national stage application ofInternational PCT Application No. PCT/US2014/051140, filedinternationally on Aug. 14, 2014, which claims the benefit of U.S.Provisional Application No. 61/866,367, filed on Aug. 15, 2013, each ofwhich is incorporated by reference herein in its entirety.

TECHNICAL FIELD

Aspects of the present disclosure relate to a flexible shaft for arobotic surgical instrument. Aspects of the present disclosure alsorelate to a robotic surgical system that includes a surgical instrumenthaving a flexible shaft with axial stiffening members.

INTRODUCTION

Benefits of minimally invasive surgery are well known, and include lesspatient trauma, less blood loss, and faster recovery times when comparedto traditional, open incision surgery. In addition, the use of roboticsurgical systems (e.g., teleoperated robotic systems that providetelepresence and computer-assisted surgical systems) are known. Anexample of a teleoperated robotic surgical system is the da Vinci®Surgical System manufactured by Intuitive Surgical, Inc. of Sunnyvale,Calif. Such surgical systems may allow a surgeon to operate withintuitive control and increased precision when compared to manualminimally invasive surgeries.

To further reduce patient trauma and to retain the benefits ofteleoperated and computer-assisted surgical systems, surgeons have begunto carry out a surgical procedure to investigate or treat a patient'scondition through a single incision through the skin. In some instances,such “single port access” surgeries have been performed with manualinstruments or with existing surgical systems. In order to moreeffectively perform single port access surgeries, surgeons andcomputer-assisted surgical systems require tools and instruments thatmaximize the surgical space accessible through a single port and thatmaximize the number of surgical instruments that can access the port atone time.

SUMMARY

Exemplary embodiments of the present disclosure may solve one or more ofthe above-mentioned problems and/or may demonstrate one or more of theabove-mentioned desirable features. Other features and/or advantages maybecome apparent from the description that follows.

In accordance with at least one exemplary embodiment, a shaft for asurgical instrument is disclosed. The shaft comprises a shaft bodyhaving a proximal end and a distal end, a drive rod extending throughthe distal end of the shaft body, and an end effector operativelycoupled to a distal end of the drive rod. The drive rod passes through apassageway in a clevis of the end effector, and the drive rod andpassage are sized such that a maximum flow of air between the passageand the drive rod is 25 cc/min of air.

In accordance with another exemplary embodiment of the presentdisclosure, a method of sealing a shaft of a surgical instrument isprovided. The method comprises positioning a drive rod in a shaft bodyof the surgical instrument, and connecting a distal end of the drive rodto an end effector of the surgical instrument. Connecting the distal endof the drive rod includes positioning the drive rod in a passageway of aclevis of the end effector, the passageway having a diameter configuredto slidingly receive the drive rod. A diameter of the drive rod isbetween about 0.0000 inches and 0.0011 inches less than the diameter ofthe passageway.

In accordance with an alternative exemplary embodiment of the presentdisclosure, a shaft for a surgical instrument comprises an outer tubehaving a proximal end and a distal end, a central lumen extendingthrough the outer tube, and a plurality of stiffening rods positionedaround the central lumen. Each of the plurality of stiffening rodscomprises a nonconductive material.

In accordance with yet another exemplary embodiment of the presentdisclosure, an electrosurgical instrument for a computer-assistedsurgical system is provided. The instrument comprises a shaft, a driverod, an electrosurgical end effector, and at least one stiffening rodconfigured to resist axial compression of the shaft during actuation ofthe end effector. The at least one stiffening rod comprises anonconductive material.

In accordance with another exemplary embodiment of the presentdisclosure, a surgical instrument comprises a shaft having an outer tubehaving a proximal end and a distal end, a drive rod, and at least fourstiffening rods positioned around the drive rod. Each stiffening rod ispositioned substantially immediately adjacent to the drive rod. Thesurgical instrument further comprises an end effector operativelycoupled to the drive rod. An axial stiffness of the shaft increasesincrementally during actuation of the end effector.

In accordance with an alternative embodiment of the present teachings, amethod of resisting axial compression in an instrument shaft isdisclosed. The method comprises applying a first force to the instrumentshaft sufficient to engage a first stiffening element contained withinthe shaft, the first stiffening element configured to resist axialcompression of the shaft, and subsequently applying additional force tothe instrument shaft sufficient to engage at least a second stiffeningelement contained within the shaft.

Additional objects, features, and/or advantages will be set forth inpart in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the present disclosureand/or claims. At least some of these objects and advantages may berealized and attained by the elements and combinations particularlypointed out in the appended claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the claims; rather the claims should beentitled to their full breadth of scope, including equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure can be understood from the following detaileddescription, either alone or together with the accompanying drawings.The drawings are included to provide a further understanding of thepresent disclosure, and are incorporated in and constitute a part ofthis specification. The drawings illustrate one or more exemplaryembodiments of the present teachings and together with the descriptionserve to explain certain principles and operation. In the drawings,

FIG. 1 is a schematic view that shows first and second curved cannulasand an endoscope for providing access to a surgical site through asingle port;

FIG. 2A is a front view of an exemplary embodiment of a portion of ateleoperated, computer-assisted surgical system;

FIG. 2B is a perspective view of a patient side manipulator with asurgical instrument mounted thereon in accordance with the presentteachings;

FIG. 3 is a side view of a flexible surgical instrument in accordancewith the present teachings;

FIG. 4A is a bottom view of an exemplary embodiment of a forcetransmission mechanism for use with a flexible surgical instrument inaccordance with the present teachings;

FIG. 4B is a plan view of an exemplary embodiment of a forcetransmission mechanism used in a push/pull flexible surgical instrumentdesign in accordance with the present teachings;

FIG. 5 is a cross-sectional side view of an exemplary push/pullinstrument in accordance with the present teachings;

FIG. 6A is a perspective view of an exemplary embodiment of a distal endof a flexible surgical instrument according to the present teachings;

FIG. 6B is a cross-sectional side view of the distal end of the flexiblesurgical instrument of FIG. 6A;

FIG. 6C is a radial cross section of the shaft of the flexible surgicalinstrument of FIG. 6A;

FIG. 6D is a perspective view of an exemplary embodiment of a proximalend of a flexible surgical instrument according to the presentteachings;

FIG. 6E is a cross-sectional side view of the proximal end of theflexible surgical instrument of FIG. 6D;

FIGS. 6F-6I are radial cross-sectional views of alternative embodimentsof a distal portion of a shaft of a flexible surgical instrument inaccordance with the present teachings;

FIG. 7 is a cross-sectional side view of an exemplary shaft of aflexible surgical instrument illustrating a flush path a shaft of theinstrument in accordance with the present teachings;

FIG. 8A is a perspective view of an exemplary embodiment of a distal endof a bipolar surgical instrument according to the present teachings;

FIG. 8B is a perspective cross-sectional view of an exemplary embodimentof a proximal end of a bipolar surgical instrument according to thepresent teachings;

FIG. 8C is a perspective view of a proximal end of a shaft portion of abipolar surgical instrument according to the present teachings;

FIG. 8D is a radial cross section of the shaft of the bipolar surgicalinstrument of FIGS. 8A-8C;

FIGS. 9A-9C are radial cross-sectional views of alternative embodimentsfor positioning the stiffening rods substantially immediately adjacentto the drive rod; and

FIG. 10 is a radial cross-sectional view of a drive rod and clevisillustrating a gap between a drive rod and a clevis of an instrumentshaft that controls leakage in the instrument shaft in accordance withthe present teachings.

DETAILED DESCRIPTION

This description and the accompanying drawings that illustrate exemplaryembodiments should not be taken as limiting. Various mechanical,compositional, structural, electrical, and operational changes may bemade without departing from the scope of this disclosure and thedisclosed subject matter as claimed, including equivalents. In someinstances, well-known structures and techniques have not been shown ordescribed in detail so as not to obscure the disclosure. Like numbers intwo or more figures represent the same or similar elements.Additionally, elements and their associated features that are describedin detail with reference to one embodiment may, whenever practical, beincluded in other embodiments in which they are not specifically shownor described. For example, if an element is described in detail withreference to one embodiment and is not described with reference to asecond embodiment, the element may nevertheless be claimed as includedin the second embodiment.

For the purposes of this specification and appended claims, unlessotherwise indicated, all numbers expressing quantities, percentages, orproportions, and other numerical values used in the specification andclaims, are to be understood as being modified in all instances by theterm “about,” to the extent they are not already so modified.Accordingly, unless indicated to the contrary, the numerical parametersset forth in the following specification and attached claims areapproximations that may vary depending upon the desired propertiessought to be obtained. At the very least, and not as an attempt to limitthe application of the doctrine of equivalents to the scope of theclaims, each numerical parameter should at least be construed in lightof the number of reported significant digits and by applying ordinaryrounding techniques.

It is noted that, as used in this specification and the appended claims,the singular forms “a,” “an,” and “the,” and any singular use of anyword, include plural referents unless expressly and unequivocallylimited to one referent. As used herein, the term “include” and itsgrammatical variants are intended to be non-limiting, such thatrecitation of items in a list is not to the exclusion of other likeitems that can be substituted or added to the listed items.

Further, this description's terminology is not intended to limit thedisclosure. For example, spatially relative terms—such as “proximal” and“distal—may be used to describe one element's or feature's relationshipto another element or feature as illustrated in the figures. Thesespatially relative terms are intended to encompass different positions(i.e., locations) and orientations (i.e., rotational placements) of adevice in use or operation in addition to the position and orientationshown in the figures. For example, the terms “proximal” and “distal” arerelative terms, where the term “distal” refers to the portion of theobject furthest from an operator of the instrument and closest to thesurgical site, such as the opening of the tool cover or the end effectorof the instrument. The term “proximal” indicates the relative proximityto the operator of the surgical instrument and refers to the portion ofthe object closest to the operator and furthest from the surgical site.In this application, an end effector refers to a tool installed at thedistal end of an instrument, including but not limited to forceps orgraspers, needle drivers, scalpels, scissors, spatulas, blades, andother tools, which may or may not use energy to cauterize tissue (i.e.,a monopolar or bipolar tool).

The term “flexible” in association with a mechanical structure orcomponent should be broadly construed. In essence, the term means thestructure or component can be repeatedly bent and restored to anoriginal shape without harm. Many “rigid” objects have a slight inherentresilient “bendiness” due to material properties, although such objectsare not considered “flexible” as the term is used herein. A flexiblemechanical structure may have infinite degrees of freedom (DOF's).Examples of such structures include closed, bendable tubes (made from,e.g., NITINOL, polymer, soft rubber, and the like), helical coilsprings, etc. that can be bent into various simple and compound curves,often without significant cross-sectional deformation. A short, flexiblestructure may serve as, and be modeled as, a single mechanicalconstraint (joint) that provides one or more DOF's between two links ina kinematic chain, even though the flexible structure itself may be akinematic chain made of several coupled links. Knowledgeable personswill understand that a component's flexibility may be expressed in termsof its stiffness.

Aspects of the present disclosure are described primarily in terms of animplementation using a da Vinci® Surgical System, manufactured byIntuitive Surgical, Inc. of Sunnyvale, Calif. Knowledgeable persons willunderstand, however, that novel aspects disclosed herein may be embodiedand implemented in various ways, including robotic and non-roboticembodiments and implementations. Implementations on da Vinci® SurgicalSystems are merely exemplary and are not to be considered as limitingthe scope of the novel aspects disclosed herein. The terms “roboticsurgical system,” “computer-assisted surgical system,”“computer-assisted medical system,” and “teleoperated surgical system”are used interchangeably herein to refer to a surgical system thatincludes aspects of computer-enabled function that may be autonomous,semiautonomous, or under direct teleoperated control. These systems mayoperate under direct manual control and/or may be teleoperated.

Various exemplary embodiments of the present disclosure contemplate acomputer-assisted surgical system including an instrument having aflexible shaft permitting use in a curved cannula system such as thoseused in a single port access surgery. Single port access surgery is atechnique in which all instruments used for minimally invasive surgeryare passed through a single incision in the patient's body wall, or insome instances through a single natural orifice. Such methods may bereferred to by various terms, such as Single Port Access (SPA), LaparoEndoscopic Single-site Surgery (LESS), Single Incision LaparoscopicSurgery (SILS), One Port Umbilical Surgery (OPUS), Single PortIncisionless Conventional Equipment-utilizing Surgery (SPICES), SingleAccess Site Surgical Endoscope (SASSE), or Natural OrificeTransUmbilical Surgery (NOTUS). Use of a single port may be accomplishedusing either manual instruments or a robotic surgical system.

An advantageous configuration for accessing a surgical site is to createa working triangle defined by the surgical site itself and the distalends of two surgical instruments. In such a configuration, the distalends of the surgical instruments are positioned along the legs of thetriangle and above the apex of the triangle, the surgical site. Insingle port access surgeries, the use of a single port constrains theangle at which a surgical instrument can access the surgical site,making it difficult to achieve the desired triangulation between thedistal ends of the surgical instruments and the surgical site itself.

One approach to maximize the surgical space available is to use a curvedcannula system. Such curved cannula systems may be used withcomputer-assisted surgical systems or with other systems such as thoseused during manual surgery. Exemplary curved cannula systems aredisclosed in detail in U.S. Published Application No. 2011/0071542 A1,published on Mar. 24, 2011, which is hereby incorporated by reference inits entirety. In contrast to the use of straight cannulas andinstruments in a single body opening, the use of curved cannulasprovides a reasonably large volume above the single incision in whichinstruments and/or robotic arms supporting instruments can move relativeto one another without collision, providing a correspondingly largervolume in which the instruments can move at the surgical site.

FIG. 1 illustrates an exemplary pair of curved cannulas positioned foruse in a single port access surgery. As shown, a port 132 may be placedin an incision 128 in a body wall 130 to provide access to surgical site124. Cannulas extend through port 132 and surgical instruments passedthrough the cannulas can access the surgical site 124. Such a port 132may have various configurations, as described in detail in U.S.Published Application No. 2011/0071542 A1, published on Mar. 24, 2011,and incorporated herein by reference in its entirety.

As shown in FIG. 1, first and second curved cannulas 116 a, 116 b eachinclude a proximal end 118 a, 118 b, a distal end 120 a, 120 b, and acentral channel 122 a, 122 b extending between proximal end 118 a, 118 band distal end 120 a, 120 b. Curved cannulas 116 a, 116 b may be rigid,single piece cannulas. FIG. 1 illustrates that curved cannula 116 bcurves in a direction opposite to the direction in which curved cannula116 a curves. The two curved cannulas and associated surgicalinstruments are positioned to extend through single incision 128 in thepatient's body wall 130 via port 128 to reach surgical site 124. Eachcurved cannula initially angles away from a straight line between theincision and the surgical site and then curves back towards the line todirect the extended instruments to the surgical site. Each curvedcannula 116 a, 116 b provides an access pathway through the single portto the surgical site for a respective surgical instrument. During use, aflexible shaft 306 a of a surgical instrument 300 a extends throughcurved cannula 116 a's central channel 122 a so that a distal portion offlexible shaft 306 a and the end effector 304 a of the surgicalinstrument extend beyond cannula 116 a′s distal end 120 a in order toreach surgical site 124.

FIG. 2A shows an exemplary teleoperated computer-assisted surgicalsystem that can be used to support and move combinations of a curvedcannula and a flexible surgical instrument to access a surgical sitethrough a single port access in accordance with an embodiment of thepresent teachings. Such a teleoperated computer-assisted surgical systemis described in U.S. Published Application No. 2011/0071542 A1,published on Mar. 24, 2011, which is hereby incorporated by reference inits entirety. Components of a teleoperated surgical system, such as aninstrument arm, carriage, instrument interface, and other components,may have the features described in U.S. Pat. No. 7,963,913, issued Jun.21, 2011, which is hereby incorporated by reference in its entirety.Such teleoperated, computer-assisted surgical systems include aprocessor and a memory.

The teleoperated computer-assisted surgical system 200 allows a surgeon,with the assistance of a surgical team, to perform diagnostic andcorrective surgical procedures on a patient. In an exemplary embodiment,a teleoperated computer-assisted surgical system in accordance with thepresent disclosure may be embodied as a da Vinci® surgical systemcommercialized by Intuitive Surgical, Inc. of Sunnyvale, Calif. However,the present disclosure is not limited to any particular teleoperatedcomputer-assisted surgical system, and one having ordinary skill in theart would appreciate that the disclosure herein may be applied in avariety of surgical applications, including other computer-assistedsurgical systems, as well as in manual surgical applications.

System 200 includes a plurality of robotic arms 206, each of whichsupports and moves a combination of a curved cannula and a flexiblesurgical instrument. Each arm 206 is made of a series of links, thelinks being coupled to one another by joints. Arm 206 is divided intotwo portions, a “set-up” portion that positions the arm relative to thesurgical site, and a patient side manipulator (“PSM”) portion thatsupports and moves the curved cannula and surgical instrument relativeto the surgical site. Flexible surgical instruments 300 can beinterchangeably mounted on the manipulator portion of arm 206. In thismanner, instruments 300 can be selected for a particular medicalprocedure or changed during a medical procedure to provide the clinicalfunctions needed.

As illustrated in FIG. 3, a flexible surgical instrument 300 generallyincludes a transmission or backend mechanism 330, a shaft 306 extendingfrom the backend mechanism 330, and a distal end effector 304 extendingfrom the distal end of the shaft 306. In some cases, a wrist (not shown)may connect shaft 306 and end effector 304. A drive rod that isconnected to end effector 304 (or to a wrist) in an instrument 300 mayextend through shaft 306 and connect to backend mechanism 330. Backendmechanism 330 typically provides a mechanical coupling of the drive rodto a drive motor in system 200. System 200 can thus control movement ofthe drive rod as needed to move or position and operate distal endeffector 304. Actuation forces may typically roll instrument shaft 306,operate a wrist to provide yaw and pitch DOF's, and operate a movablepiece or grasping jaws of various end effectors (e.g., scissors (cauteryor non-cautery capable), dissectors, graspers, needle drivers,electrocautery hooks, retractors, clip appliers, etc.). According to anexemplary embodiment, surgical tools may be arranged according to theembodiments described in U.S. Pat. No. 6,817,974, issued Nov. 16, 2004,and U.S. Pat. No. 6,394,998, issued May 28, 2002, which are herebyincorporated by reference in their entirety.

System 200 also includes a camera arm 208 that supports and moves acamera system 212 such as an endoscope for viewing of a surgical siteand the operation of instruments 300 within a patient. The views fromthe camera system, which may be stereoscopic or three-dimensional, canbe viewed at a control console (not shown) and images may be displayedon a monitor (not shown). A processing system of system 200 can thusprovide a user interface enabling a doctor or other medical personnel tosee and manipulate the camera system and surgical instruments.

As illustrated in FIG. 2B, the patient side manipulator portion of arm206 includes a carriage an instrument docking area 220 for releasablyreceiving a surgical instrument 300. Generally, the instrument dockingarea 220 releasably connects to a transmission mechanism 330 of surgicalinstrument 300. The PSM may include one or more drive motors thatprovide mechanical power for operation of surgical instruments 300. Inaddition, PSM may include an electrical interface for communication witha surgical instrument 300. Such communication may include reading amemory of a transmission mechanism 330 of a surgical instrument 300.Data included on the memory may include, for example, parametersrelevant to a surgical instrument and its operation such as the type ofinstrument and/or specific characteristics of the instrument. Highvoltage electrical systems (not shown) such as generators forcauterizing or sealing instruments would typically connect to suitableinstruments 300 through separate connectors but could alternatively beprovided through built-in circuits in control system 200.

FIG. 4A is a bottom view of an exemplary embodiment of a forcetransmission mechanism 430. As shown in FIG. 4A, the force transmissionmechanism 430 of a surgical instrument (not shown) used in ateleoperated surgical system has been modified to eliminate themechanisms used to control a wrist mechanism on the instrument and tocontrol the jaw of an end effector (or other moveable part) using only asingle interface disk. Thus, in one illustrative implementation, oneinterface disk 402 a rolls a shaft 306 of an instrument so as to providea roll DOF for an end effector, and a second interface disk 402 b mayoperate a jaw mechanism of an end effector to open and close the jawmechanism. Force transmission mechanism 430 may be coupled to a PSMwithout any mechanical modifications required to the PSM, a feature thatminimizes implementation costs of curved cannula aspects in existingteleoperated surgical systems. Further, each instrument may include aforce transmission mechanism that permits control of the specificinstrument without change to the interface between the PSM and theinstrument.

Force transmission mechanism 430 may include electrically conductiveinterface pins 404 and an electronic data memory 406 that iselectrically coupled to interface pins 404. Parameters relevant to asurgical instrument and its operation (e.g., number of times theinstrument has been used, Denavit-Hartenberg parameters for control(described below), etc.) may be stored in memory 406 and accessed by thecomputer-assisted surgical system during operation to properly use theinstrument (see e.g., U.S. Pat. No. 6,331,181 (issued Dec. 18, 2001)(disclosing surgical robotic tools, data architecture, and use), whichis incorporated herein by reference in its entirety). Use of forcetransmission mechanisms for push/pull type instruments also is disclosedin U.S. Provisional Application No. 61/823,688 entitled “ForceTransmission Mechanisms for Robotic Surgical Systems,” filed May 15,2013, the contents of which is incorporated herein by reference in itsentirety.

In one implementation, kinematic data specific to a cannula throughwhich the instrument extends may also be stored in memory 406, so thatif the teleoperated surgical system detects that a particular cannula ismounted, the system may access and use the stored cannula data. If morethan one cannula kinematic configuration (e.g., different lengths, bendradii, bend angles, etc.) is used, then data specific to each allowableconfiguration may be stored in the associated instrument's memory, andthe system may access and use data for the specific cannulaconfiguration that is mounted. In addition, if during a single portaccess surgery the robotic surgical system senses that an instrumentintended for use with a curved cannula has been coupled to a manipulatorthat holds a straight, rather than curved, cannula, then the system maydeclare this situation to be an illegal state and prevent operation.

FIG. 4B is a plan view of an exemplary embodiment of a forcetransmission mechanism used in a push/pull instrument design. As shownin FIG. 4B, a push/pull drive element rod 326 extends out of a proximalend of the instrument shaft 306, and further extends through a backingplate 442 to be coupled with slider 446. In this implementation, driveelement rod 326 is coupled with linear slider 446 using a free rollingbearing 448. This free rolling bearing prevents the drive rod fromtwisting when the instrument shaft is rolled (i.e., provides anunconstrained roll DOF). Push/pull drive gear 450 is engaged with levergear 452. Lever gear 452 is coupled to slider 446 with link (offsetcrank) 454. As drive gear 450 turns back and forth as indicated byarrows 456, slider 446 slides along shaft 458 as indicated by arrows460, thus moving drive element 326 along the instrument shaft'slongitudinal axis. FIG. 4B also shows a cross-connected helical drivegear 420 and a shaft roll gear 422. Roll gear 422 is coupled (e.g.,laser welded) to a stainless steel adaptor swaged over the proximal endof the flexible shaft's body.

In accordance with the present teachings, a surgical instrument to beused in a single port access surgery and intended to pass through acurved cannula includes a flexible shaft. The shaft is relativelyflexible to reduce friction with the inner wall of the curved cannula,yet it is not made so flexible so that it buckles during insertionthrough the curved cannula under manual or servo-controlled operation.While flexibility of the shaft is important, the shaft must be rigidenough to provide adequate cantilever support for the end effector(surgical tool). For instruments that require an end effector roll DOFvia shaft roll, the shaft is torsionally rigid enough to transmit rollmotion from the proximal end of the instrument to distal surgical endeffector.

In particular, for any given bend radius of a curved cannula, a bendingstiffness of a shaft in accordance with the present teachings fallswithin a range that balances the necessary flexibility to pass throughthe curved cannula with the stiffness required to apply useable force tothe instrument end effector. Within this range, which varies dependentupon the curvature of the cannula to be traversed, the axial stiffnessof the shaft is maximized through manipulation of various elements ofthe shaft, including geometry of the shaft elements and materialselection for those elements. The manner in which stiffening elements inthe shaft are positioned within the shaft and are connected orunconnected to the shaft also affect shaft stiffness. For example, inaccordance with the present teachings, stiffening elements positionedwithin the shaft may not be physically connected to the shaft be simplysit or “float” within the shaft, minimizing the number of stiffeningelements that are loaded during initial bending of the shaft and thuscontribute to the overall bending stiffness of the shaft.

Various design aspects may be used for the flexible instrument shafts.The following descriptions disclose example implementations of flexibleshafts used for instruments with a movable end effector component, andit should be understood that the principles described (e.g., ways ofstiffening) may be adapted for shafts that do not have an end effectorwith a moving component. It should also be understood that theprinciples may be adapted to instrument aspects that include a movablewrist mechanism or other mechanism at the distal end of the instrumentshaft.

Surgical instrument end effectors placed at the distal end of theflexible shaft instruments are of two general types. The first type ofend effector has no moving parts. Such non-moving end effectors mayinclude, for example, suction/irrigation tips, electrocautery hooks orblades, probes, blunt dissectors, cameras, retractors, etc. The secondtype of end effector has at least one moving component that is actuatedunder computer-assisted control. Such moving component end effectorsinclude, for example, graspers, needle drivers, moving cautery hooks,clip appliers, shears (both non-cautery and cautery), etc.

As disclosed herein, end effector component(s) are actuated by a singlecompression/tension element that moves the end effector component. Insuch a “push/pull” design, pulling (tension) is used to move thecomponent in one direction, and pushing (compression) is used to movethe component in the opposite direction. In some implementations, thetension force is used to actuate the end effector component in thedirection that requires the highest force (e.g., closing jaws). Placingthe push/pull drive rod in tension may increase axial compression of theinstrument shaft during actuation of the end effector. Alternativemechanisms for actuating an end effector are known and discussed in U.S.Published Application No. 2011/0071542 A1, published on Mar. 24, 2011,and incorporated herein by reference.

Design considerations for a suitable instrument shaft include bendingstiffness and axial stiffness of the instrument shaft. In particular, itis desirable to maximize the axial stiffness of the shaft (i.e., toprovide resistance to axial compression of the shaft and support for theend effector) while minimizing the bending stiffness of the shaft (e.g.,to permit ease of access through the curved cannula and the single portto the surgical site). Maximizing axial stiffness of the shaft (i.e.,maximizing resistance to axial compression of the shaft) allows moreefficient transfer of force from a drive element of the shaft to the endeffector and may facilitate tighter control of the end effector byminimizing undirected movement of the end effector during actuation ofthe drive element. Other design considerations such as materials usedand their characteristics (e.g., flexural modulus, tensile strength,coefficient of friction, etc.), dimensions of elements (e.g., drive rod,stiffening rod, etc.) contained within the shaft, and placement ofelements in relation to each other allow variations of and interplaybetween the bending stiffness and the axial stiffness of an instrumentshaft in accordance with the present teachings.

FIG. 3 is a diagrammatic view of an exemplary flexible instrument 300used with a curved cannula 116. Instrument 300 includes a proximal endforce transmission mechanism 330, a distal end surgical end effector304, and a shaft 306 that couples force transmission mechanism 330 andend effector 304. The shaft may range between 30 cm and 60 cm in length,and in one implementation, shaft 306 is about 43 cm in length. The shaft306 may have the same axial stiffness along its length. Alternatively,the shaft may vary in stiffness along its length to accommodatedifferent portions of a curved cannula. Examples of variations in thestiffness of the shaft are discussed in detail in U.S. PublishedApplication No. 2011/0071542 A1, published on Mar. 24, 2011, andincorporated herein by reference.

FIG. 5 is a cross-sectional side view of an exemplary surgicalinstrument that illustrates aspects of a push/pull instrument design. Asshown in FIG. 5, an instrument force transmission mechanism 530 iscoupled to a grip-type end effector 504 by a flexible shaft body 506. Acompression/tension drive element 526 is routed through shaft body 506and couples a movable component in end effector 504 to a component (notshown; see description of FIGS. 4A and 4B above) in transmissionmechanism 530 that receives a robotic actuation force. When the driverod 526 is actuated (i.e., placed in tension), the push/pull drive rodcompresses substantially the entire shaft 506 of instrument 500. Inorder to offset the compression loads on the shaft 506, one or moreaxial stiffening rods are provided within the body of shaft 506. Thestiffening rods are radially spaced from the drive rod and evenly spacedaround drive rod to surround the drive rod. Each stiffening rod ispositioned in the shaft, between the force transmission mechanism andthe end effector of the instrument. The stiffening rods are not,however, anchored within or otherwise connected to ends of the shaft andinstead float freely within the shaft. Allowing the stiffening rod(s) tofloat within the shaft reduces the effect such rods have on the bendingstiffness of the flexible shaft. In addition, in cases where more thanone stiffening rod is provided, because the stiffening rods float withinthe shaft, only a single stiffening rod is actuated or engages duringinitial bending of the drive rod or as drive rod is initially actuated.When the shaft 506 is bent, a stiffening rod along the shortest pathbetween ends of the shaft 506 engages both ends of the shaft 506,thereby providing resistance to axial compression of the shaft 506. Insuch a bent shaft, there is a differential length between the pathsalong which the engaged stiffening rod passes and paths that otherstiffening rods pass. The difference in length along these paths may beminimized by, for example, by positioning the stiffening rods closer tothe center of the multi-lumen shaft 506 and drive rod 526. Such aconfiguration may provide greater control over the instrument and endeffector.

As the shaft rolls, the stiffening rod along the shortest path of theshaft changes, changing the stiffening rod that contributes to the axialstiffness of the shaft. As the drive element (push/pull rod or driverod) is actuated, it may be placed in tension (pulling) or compression(pushing). As the drive rod is actuated under tension, it compresses theshaft 506 and, thus, the path lengths of the stiffening rods shorten.The arrow in FIG. 5 represents the axial compression of the shaft alongthe longitudinal axis of the shaft during actuation of the end effector.As the path lengths shorten, additional stiffening rods are engaged tofurther resist axial compression of the shaft 506. During bending of theshaft, the stiffening rods float within the shaft body and do not pullagainst either end of the shaft of the instrument. The lack ofadditional forces created during bending of the shaft reduces theoverall bending stiffness of the shaft. Although the presence of thestiffening rods does contribute the overall bending stiffness of theshaft, this contribution can be further minimized by controlling designaspects of the stiffening rods, such as the diameter of the stiffeningrods, the material from which the rods are made, etc.

Shaft body materials have an elastic modulus (or Young's modulus) lowenough to allow bending with low enough radial force to limit frictioninside a curved cannula so that instrument insertion and withdrawal isnot affected in a meaningful way, but its modulus of elasticity is highenough to provide good cantilever beam stiffness for a distal portion ofthe surgical instrument (shaft and end effector) that extends beyond thedistal end of the curved cannula, to resist buckling of any portion ofthe shaft between the transmission mechanism and the proximal end of thecannula, and to transmit roll motion and torque along the length of theinstrument shaft with adequate stiffness and precision.

For example, the bending stiffness of an instrument shaft in accordancewith the present disclosure may be modeled using the bending stiffnessof an outer/main tube of the shaft, the bending stiffness of the driverod of the instrument, and the bending stiffness of stiffening rods usedto provide axial strength to the instrument shaft. The bending stiffnessfor a drive rod or a stiffening rod (K_(bend) _(rod) ) may be modeledusing the following formula:K _(bend) _(rod) =E*I  (1)where E=flexural modulus and I=area moment of inertia of cross-sectionof the rod. The area moment of inertia can be calculated using theformula:

$\begin{matrix}{I_{rod} = \frac{\pi*r^{4}}{4}} & (2)\end{matrix}$where r=the radius of the rod. The bending stiffness and area moment ofinertia of cross-section of the outer or main body tube of the shaft maybe calculated in the same manner used for the rod, but accounting forthe hollow cross section of the tube in the area moment of inertia usingthe formula:

$\begin{matrix}{I_{{main}\mspace{14mu}{body}\mspace{14mu}{tube}}=={\frac{\pi}{4}*\left( {r_{o}^{4} - r_{i}^{4}} \right)}} & (3)\end{matrix}$where r_(o) is the outer radius of the outer/main tube and r_(i) is theinner radius of the outer or main body tube. Once the bending stiffnessof the drive rod and of any stiffening rods have been calculated, aswell as the bending stiffness for the outer or main body tube, thebending stiffness for the instrument shaft (K_(bend) _(shaft) ) can bemodeled using the following formula:K _(bend) _(shaft) =K _(bend) _(main body tube) +K _(bend) _(drive rod)+N*K _(bend) _(stiffening rod)   (4)where K_(bend) is bending stiffness and N is the number of stiffeningrods contained in the shaft. Although the bending stiffness of themultilumen tube (K_(bend) _(multilumen) ) technically contributes to thebending stiffness of the shaft, it is negligible for practical purposesand has for this reason is not listed equation (4) above. However, asone of skill in the art will understand, the selection of materials usedfor the multi-lumen tube may render this variable more impactful on theoverall bending stiffness.

In a flexible shafted instrument in accordance with the presentteachings, the goal is to identify a bending stiffness of the shaft,K_(bend shaft), that is substantially equal to the bending stiffness ofthe main body tube of the shaft, K_(bend) _(main body tube) . That is,the bending stiffness of the stiffening rod(s) should minimallycontribute to the overall bending stiffness of the shaft whilemaximizing the axial stiffness of the shaft. By selecting a materialwith a high tensile modulus (c) for the stiffening rod, the axialstiffness of the instrument shaft is increased. By selecting a smallradius for the stiffening rods (significantly smaller than 0.1 cm), thearea moment of inertia is very small which reduces the additionalbending stiffness added by the stiffening rods. For example, thediameter range for stiffening elements made from stainless steel mayrange between 0.5 mm and 1.25 mm. The diameter range for stiffeningelements will depend upon the particular materials selected as well asthe degree of curvature of the cannula to be traversed.

As discussed above, only one stiffening rod contributes to the axialstiffness of the shaft of the surgical instrument during bending of theshaft (the stiffening rod along the shortest path in the shaft as theshaft is placed in tension or compression is loaded in a curvedinstrument, the other wires are floating). During bending of the shaft,the axial stiffness of the shaft is substantially equal to the sum ofthe axial stiffness of the outer tube and one stiffening rod when theend effector is not being actuated by the drive rod. As actuation of theend effector proceeds, the shaft is compressed shortening the pathlength of the remaining stiffening rods, allowing additional stiffeningrods to engage and, thus, gradually increasing the axial stiffness ofthe shaft as the additional stiffening rods engage. Such engagement maybe substantially simultaneous or it may be gradual as the additionalstiffening rods are consecutively engaged. When the drive rod is fullyloaded such that all stiffening rods are engaged, the axial stiffness ofthe shaft is equal to the sum of the outer tube axial stiffness and thetotal stiffness of the plurality of stiffening rods Any support tubeprovided within the shaft body, for example to align the stiffening rodsand/or providing flush channels, also may be unanchored or free floatingwithin the shaft so as not to contribute to the axial stiffness of theshaft. For the same reasons, such a support tube may have a lengthshorter than that of the axial stiffening rods such that it will notengage when the stiffening rods engage. Additionally or alternatively,the support tube may be made from materials having substantially loweraxial stiffness.

The axial stiffness of the drive rod and the axial stiffness of astiffening rod may each be determined using the following formulas:

$\begin{matrix}{K_{axial} = \frac{ɛ*A}{L}} & (5)\end{matrix}$and A _(rod) =π*r ²  (6)

where K_(axial) is the axial stiffness, ε is the tensile modulus of thematerial used for the drive rod or stiffening rod, A_(rod) is thecross-sectional area of the drive rod or stiffening rod, L is the lengthof the drive rod or stiffening rod, and r is the radius of the drive rodor stiffening rod. The axial stiffness of the main body tube of theshaft may be determined using the following formulas:

$\begin{matrix}{K_{{axial}_{{main}\mspace{14mu}{body}\mspace{14mu}{tube}}} = \frac{ɛ*A}{L}} & (7)\end{matrix}$and A _(main body tube)=π*(r _(o) ² −r _(i) ²)  (8)

where r_(o) is the outer radius of the outer/main tube and r_(i) is theinner radius of the outer or main body tube.

Using the axial stiffness values for the drive rod, the main body tubeof the shaft, and the stiffening rod, the axial stiffness of theinstrument shaft, K_(axial) _(shaft) may be modeled using the followingformula:

$\frac{1}{K_{{axial}_{shaft}}} = {\frac{1}{K_{{axial}_{{drive}\mspace{14mu}{rod}}}} + {\frac{1}{K_{{axial}_{{main}\mspace{14mu}{body}\mspace{14mu}{tube}}} + K_{{axial}_{{stiffening}\mspace{14mu}{rod}}}}.}}$

In the above equation, the axial stiffness of the instrument shaft ismodeled for one (1) engaged stiffening rod. If additional stiffeningrods are to be engaged, their axial stiffness would need to be accountedfor the above equation.

Using the modeled values for the bending stiffness of the instrumentshaft, K_(bend) _(shaft) , and the axial stiffness of the instrumentshaft, K_(axial) _(shaft) , it is possible, through shifting variablessuch as materials used, size of elements, etc. to minimize the bendingstiffness of the instrument shaft while providing sufficient axialstrength to the instrument shaft to support the end effector duringsurgical use.

It is possible to vary both the axial stiffness and the bendingstiffness of the shaft in accordance with the intended use of thesurgical instrument. For example, in some implementations, use of arobotic surgical system permits the bending stiffness of the instrumentshaft (or at least the portion of the shaft that moves within thecannula) to be substantially greater than an instrument shaft intendedto be wielded manually. The robot can, in certain instances, applyforces to insert an instrument shaft through a curved cannula andcontrol movement of that instrument, e.g., through roll of theinstrument, that are substantially higher than forces that can bereasonably controlled by a human. The ability to apply greater forcesvia robot permits an instrument shaft to have a bending stiffnesssubstantially higher than hand-operated instrument shaft stiffness wouldbe for a similar but manually actuated curved cannula system. Thischaracteristic enables the use of a curved cannula robotic surgicalsystem in situations in which hand-operated instruments acting throughcurved cannulas may be marginally functional or non-functional (e.g.,the hand-operated shaft stiffness is too low to enable the instrument toeffectively work at the surgical site). And so, in some implementations,the instrument shaft is “tuned” (e.g., by selecting one or moreparticular materials and/or by various shaft constructions using theselected material(s)) to (i) make effective use of the robot's insertionand roll drive capabilities with reasonably stiff shafts while (ii) notallowing the friction between such reasonably stiff shafts and aparticular cannula curve dimension to offset the robot's drivecapability benefits. Thus certain instruments may have flexible shaftswith a first bending stiffness and first axial stiffness for use withcannulas with one curve radius and/or inner diameter, and otherinstruments may have shafts of another bending stiffness and anotheraxial stiffness for use with cannulas with another curve radius and/orinner diameter. Various permutations of the axial stiffness and thebending stiffness may be incorporated into a flexible instrument shaft,depending upon the intended use of the instrument, in accordance withthe present teachings.

For example, for a particular shaft diameter and assuming cannula curveradius and cannula-shaft friction vary inversely, shaft bendingstiffness for an instrument designed for use with a cannula having arelatively larger curve radius may be greater than shaft bendingstiffness for an instrument designed for use with a cannula having arelatively smaller curve radius. Cannulas having specific curve anglesand bend radii may be used for particular surgical procedures. Forexample, one cannula length, curve angle, and bend radius may be bestsuited for reaching from a particular incision point (e.g., at theumbilicus) towards one particular anatomical structure (e.g., the gallbladder) while another cannula length, bend angle, and/or bend radiusmay be best suited for reaching from the particular incision pointtowards a second particular anatomical structure (e.g., the appendix).And, in some implementations two cannulas each having different lengthsand/or bend radii may be used. In such cases, it may be desirable tohave surgical instruments with shafts of various bending stiffnesses andaxial stiffnesses in order to maximize both access to the surgical siteand mobility and usefulness of the end effector working through eachcannula.

In various aspects, the shaft's bending stiffness (this may also bereferred to as a lateral stiffness of the shaft) is in a range fromabout 1 lb-in² (PSI×in⁴) to about 4 lb-in², and in one implementationthe shaft's lateral stiffness is about 2.0 lb-in². With regard to theaxial stiffness of the shaft, the larger the tensile or compressiveforce applied to the instrument via the drive rod, the greater the axialstiffness of the shaft should be to offset those applied forces. Forexample, in accordance with the present teachings, a drive rod may applya force of between 2 lb. and 30 lb. to the instrument, depending uponthe particular instrument end effector and clinical load on the endeffector. To accommodate such forces, each stiffening rod, in accordancewith the present teachings, may provide an axial stiffness of betweenabout 500 lb/in to about 800 lb/in (or, said another way, eachstiffening rod may resist between about 500 lb/in to about 800 lb/in ofaxial compression of the shaft). Thus, as the compressive force appliedby the drive rod increases, the number of stiffening rods that engageincreases, effectively resisting axial compression of the shaft causedby the actuation.

Examples of instrument shafts in accordance with the present teachingsare described in reference to FIGS. 6A-6E below. FIG. 6A is aperspective view of a distal end of a flexible surgical instrument inaccordance with the present teachings. FIG. 6B is a cross-sectional sideview of the distal end of the flexible surgical instrument of FIG. 6Aand FIG. 6C is a radial cross section of the shaft of the flexiblesurgical instrument of FIG. 6A.

As shown in FIG. 6A, a surgical instrument 600 includes a flexible shaft606. Shaft 606 includes an outer or main body tube that forms a shaftbody 624. Through this description, the terms “outer body tube” and“main body tube” are used interchangeably. Shaft body 624 provides axialand torsional stiffness to shaft 606. The inner and outer diameters ofshaft body 624, as well as the material used for shaft body 624, areselected to provide a desired bending stiffness of the shaft body 624.Shaft body 624 may be made, for example, of a high stiffness plastic. Inone exemplary embodiment, shaft body 624 is made of polyether etherketone (PEEK). Other suitable materials such as an aliphatic polyamide(nylon) which can be glass or carbon filled, polyetherimide (PEI) whichcan be glass or carbon filled, thermoplastic elastomers (TPE) such aspolyether block amide (PEBA) which can be reinforced, and epoxy andcarbon fiber and epoxy and glass fiber pultruded tubes may be used forshaft body 624. Materials may be selected such that the shaft body 624is autoclavable or is disposable. Shaft body 624 may have an outerdiameter, for example, of about 5 mm, and an inner diameter of about 3.5mm. Alternatively, depending upon the size of the curved cannulaprovided, and the number of cannulas to be used through the single portaccess, shaft outer diameters of 3 mm or 8 mm may be used, withrespective inner diameters of 1 mm to 7 mm.

As illustrated in FIG. 6A, shaft body 624 may include an outer skin orouter coating 634. Outer skin or coating 634 surrounds shaft body 624and reduces friction between shaft 606 and an interior of a curvedcannula as shaft 606 slides within the curved cannula. A heat shrinkmaterial such as ethylene tetrafluoroethylene (ETFE) may be used to formouter skin 634. Alternatively, other suitable materials may be used. Theouter skin or outer coating 634 is generally a thin coating, forexample, a coating of about 0.005 inches.

Within shaft body 624, a multi-lumen tube 644 provides support andalignment for a push/pull drive rod 626 of the surgical instrument 600.Multi-lumen tube 644 includes a central lumen 646 through whichpush/pull drive rod 626 extends. Multi-lumen tube 644 may includeseveral lumens 648 radially spaced from central lumen 646. Multi-lumentube 644 may be made from a soft flexible plastic such as a low frictionTeflon or a fluorinated polymer. In one exemplary embodiment,multi-lumen tube 644 comprises a fluorinated ethylene propylene (FEP)extrusion. FEP provides a low-friction surface against which elementswithin the lumens slide. Alternatively, other suitable materials such asethylene tetrafluoroethylene (ETFE) or polytetrafluoroethylene (PTFE)may be used. Multi-lumen tube 644 is not anchored within shaft body 624,and multi-lumen tube 644 is shorter in length than shaft body 624, suchthat multi-lumen tube 644 is moveable or “floats” within shaft body 624.

As illustrated in FIGS. 6A and 6C, multi-lumen tube 644 may have a lobedcross section. Although illustrated in the exemplary embodiment of FIGS.6A and 6C as having four semi-cylindrical lobes (semi-circular in crosssection), it should be understood that the “lobes” are not so limited inshape and may have any suitable shape, such as rectangular, triangular,square, etc., as illustrated in FIGS. 6F-6I. The number of lobes may beselected to correspond to the number of stiffening rods, although it ispossible that certain structures may have lobes configured to supportmore than one stiffening rod. Additionally, the shapes of the lobes mayhave corners, straight edges, or rounded edges, and such design featuresmay be selected based in part on the desired bending stiffness of theshaft. Certain shapes may be desirable for providing additional spacewithin shaft body 624 to pass additional elements through the shaft,such as wires, or to provide a fluid flush path. Additionally oralternatively, certain shapes may provide for different positioningand/or spacing of the stiffening rods 628 relative to the drive rod 626.

As illustrated in FIGS. 6A-6E, push/pull drive rod 626 extends throughthe center of multi-lumen tube 644 and is slidably moveable withincentral lumen 646 of multi-lumen tube 646. In such a “push/pull” design,pulling (tension) is used to move the component in one direction, andpushing (compression) is used to move the component in the oppositedirection. In some implementations, the tension force is used to actuatethe end effector component in the direction that requires the highestforce (e.g., closing jaws). Push/pull drive rod 626 may be made from anysuitable material, such as for example, stainless steel. Additionalsuitable materials include, for example, aluminum, carbon fiber, andNITINOL. The push/pull drive rod 626 must be made of a material and of asize sufficient to withstand the tensile and compressive forces appliedduring actuation of the end effector. Generally, the drive rod may besubjected to a load of between about 2 lb. and 30 lb. during tensionand/or compression. In accordance with the present teachings, a solidstainless steel drive rod may have an outer diameter of between 0.5 mmand 1.25 mm. In one exemplary embodiment, push/pull drive rod 626 is asolid rod, made of 304 stainless steel (stainless spring steel), with anouter diameter of 0.032 inches. Diameters will vary depending upon thematerial selection.

As shown in FIGS. 6A-6E, one or more stiffening rods 628 are provided toincrease axial stiffness of shaft 606. The number, size, and compositionof stiffening rods 628 may be selected to provide a desired axialstiffness to shaft 606 while minimizing the impact on the bendingstiffness of shaft 606 (i.e., without increasing the bending stiffness).Like multi-lumen tube 644, stiffening rods 628 are not anchored withinshaft body 624 and are free to move or float within shaft body 624.Because stiffening rods 628 float within multi-lumen tube 644 and shaftbody 624, only a single stiffening wire contributes to the bendingstiffness of the instrument shaft 606. When the shaft 606 is bent, astiffening rod along the shortest path between ends of the shaft 606 isthe stiffening rod that is engages and increases the axial stiffness ofthe shaft 606. As the shaft rolls, the stiffening rod along the shortestpath of the shaft changes, changing the stiffening rod that contributesto the axial stiffness of the shaft. During bending of the shaft,multi-lumen tube 644 continues to float within shaft body 624 and isshorter than stiffening rods 628 such that it does not engage andcontribute to the axial stiffness of the shaft 606.

During actuation of the drive rod 626, the push/pull drive rodcompresses substantially the entire shaft 606 until a first one of thestiffening rods 628 engages. As additional force is applied via driverod 626, the shaft 606 continues to compress, shortening the paths ofthe stiffening rods within shaft 606. This allows additional ones of thestiffening rods to be engaged to resist axial compression of the shaft606.

As illustrated in the exemplary embodiment of FIGS. 6A-6C, fourstiffening rods 628 may be radially spaced from push/pull drive rod 626and evenly spaced from each other to surround push/pull drive rod 626.The distance the stiffening rods 628 are spaced from push/pull rod 626may be varied based on the materials used for the drive rod andstiffening rods and the dimensions of each. In some cases, increasingdistance between the push/pull drive rod 626 and stiffening rods 628 maytranslate to a slack feel, a slip, or lack of responsiveness in theinstrument. Moving the stiffening rods closer to the push/pull drive rod626 and the center of the instrument shaft minimizes the differentiallength between the stiffening rods during bending of the instrumentshaft and may improve responsiveness of the instrument (end effector)during use.

In one exemplary embodiment, the stiffening rods 628 may be positionedsubstantially immediately adjacent to the drive rod or drive rod channelin the multi-lumen tube 644. As noted above, this reduces the pathlength change during actuation of the end effector and more effectivelytransfers force from the drive rod 626 to the end effector, therebyoffering additional control over movement of the end effector.

Exemplary configurations for positioning the stiffening rods 628substantially immediately adjacent to the drive rod 626 are shown inFIGS. 9A-9C. As shown in FIG. 9A, a thin sheath 627 may surround driverod 626 to facilitate sliding of drive rod 626 relative to stiffeningrods 628, which are shown in sliding contact with sheath 627 andsubstantially immediately adjacent to drive rod 626. Stiffening rods 628may be positioned within a second sheath or multi-lobed tube 644 a tohold the stiffening rods 628 in position relative to drive rod 626. FIG.9B illustrates an exemplary embodiment in which drive rod 626 andstiffening rods 628 are in sliding contact with one another. A sheath644 b may hold stiffening rods 628 in position relative to drive rod 626while permitting sufficient space to allow relative movement betweendrive rod 626 and stiffening rods 628. In FIG. 9C, drive rod 626 ispositioned within a sheath or lumen 627 and each stiffening rod 628 ispositioned within a sheath 644 c, with sheaths 644 c positioned incontact with sheath 627 to place stiffening rods 628 substantiallyimmediately adjacent drive rod 626. Sheaths 627 and 644 c may bedesirable for permitting relative movement between drive rod 626 andstiffening rods 628 and/or for providing a fluid flush path. Otherembodiments in which the stiffening rods 628 are positionedsubstantially immediately adjacent to drive rod 626 will be understoodfrom the present teachings and examples.

Each stiffening rod 628 passes through a respective lumen 648 ofmulti-lumen tube 644. Although the exemplary embodiment of FIGS. 6A-6Cdiscloses four stiffening rods 628, it should be understood that more orless than four stiffening rods may be used. As discussed above, duringbending of shaft 606, only a single stiffening rod contributes to theaxial stiffness of the shaft, the stiffening rod that is along ashortest path between ends of the shaft. In accordance with oneexemplary embodiment, the stiffening rods each may have a diameter equalto a diameter of push/pull drive rod 626. In addition, each stiffeningrod may be made of the same material as push/pull drive rod 626, such asstainless steel 304. Other suitable materials such as aluminum, nitinol,or materials commonly used for spring elements may be used.

Stiffening rods 628 need not have a circular cross-sectional shape, andindeed may have any other suitable cross-sectional shapes, such as forexample, a square or triangular shape. Additionally or alternatively,each stiffening rod 628 may comprise a single rod or a plurality orbundle of rods. In an exemplary embodiment in which more than fourstiffening rods are used, a plurality of stiffening rods sufficient tosubstantially form a circle or perimeter around push/pull drive elementmay be used. Additionally or alternatively, in place of stiffening rodswhich surround push/pull drive rod 626, a single tube may be used tosurround push/pull drive rod 626 and increase the axial stiffness of theinstrument shaft 606. Examples of tubular elements that may be used toincrease axial stiffness of the instrument shaft 606 include a coilpipe, a hypotube, a helical hollow strand (HHS® Tube), a laser cut tube(examples of which are disclosed in U.S. Patent Application PublicationNo. 2012/0123395 A1, published on May 17, 2012, the contents of whichare incorporated herein by reference), a braided tube, a torque tube(examples of which are disclosed in U.S. Patent Application PublicationNo. 2012/0215220 A1, published on Aug. 23, 2012, the contents of whichare incorporated herein by reference), and other tubular elements havingsuitable stiffness. While use of a larger number of stiffening rods, oruse of a tubular element to surround the drive rod may increase axialstiffness of the instrument and potentially improve instrumentresponsiveness, this must be balanced against the increase in bendingstiffness contributed by each additional stiffening rod.

FIGS. 6A and 6B show that a distal end of multi-lumen tube 644terminates in a distal multi-lumen end cap 666. As shown in FIG. 6B,distal end cap 666 fits inside the distal end of shaft body 624 andpush/pull drive rod 626 extends through distal end cap 666 into an endeffector clevis 668. Both distal end cap 666 and clevis 668 may be made,for example, of a glass-filled plastic. As illustrated in FIG. 6B,multi-lumen tube 644 does not completely fill the distal end cap 666.Instead, axial stiffening rods extend out of multi-lumen tube 644 andabut the inner surface of the distal end cap 666, creating a space 670within end cap 666 between the distal end of multi-lumen tube 644 andthe inner surface of the end cap 666.

A push/pull drive rod end effector connector 672 couples with themovable component of the end effector 604. End effector clevis 668 fitsover the end of shaft body 624 and may be swaged to shaft body 624. Insome embodiments, a silicone seal (not shown) is provided between theend cap 666 and the clevis 668 or between the clevis 668 and the endeffector 604 to minimize leakage between the drive rod 626 and the endeffector 604.

In another exemplary embodiment, a seal is not provided between the endcap 666 and the clevis 668. Instead, potential leakage between the driverod 626 and the end effector 604 is controlled by minimizing a gapbetween the drive rod 626 and a passage 668 a in clevis 668 throughwhich the drive rod 626 passes. As illustrated in FIG. 10, the gap 669is the difference in diameters between the drive rod 626 and the passage668 a in the clevis 668. The use of very small tolerances creates thesmall gap 669 that permits a controlled leakage rate, for example, aleakage rate of less than 25 cc/min of air. The gap 669 between thedrive rod 626 and the passage 668 a within the clevis 668 is betweenabout 0.0000 and 0.0011 inches. A length of the gap 669 (or length ofthe seal (i.e., length of the passage 668 a in the clevis 668 throughwhich the drive rod 626 passes)) is about 0.050 inches. Elimination of aseal reduces manufacturing steps. In addition, use of a silicone seal,for example, creates the potential for the seal to be damaged or wearout and require replacement. Further, by managing the size of the gap669 and the type of material used for the clevis 668 (e.g., ahydrophobic material) it is possible to minimize potential leakagearound the drive rod 626 and clevis 668 to a rate lower than thatpermitted by a silicone seal. Although discussed herein with regard toan instrument shaft containing stiffening rods and other elements, itshould be understood that this method of sealing using a gap between thedrive rod and the passage in the rigid material forming the clevis maybe used for any instrument that utilizes a push/pull drive rod asdiscussed herein.

FIG. 6D is a perspective view of an exemplary embodiment of a proximalend of a flexible surgical instrument according to the presentteachings. FIG. 6E is a cross-sectional side view of the proximal end ofthe flexible surgical instrument of FIG. 6D.

As shown in FIG. 6D, the proximal end of multi-lumen tube 644 terminatesin a proximal end cap 674. Proximal end cap 674 fits inside a proximalend assembly 662 of instrument 610. As illustrated in FIGS. 6D and 7,drive rod 626 extends from the transmission mechanism 430 (see FIG. 4B)through roll gear 622 and proximal end assembly 662 into the proximalend of shaft 606. Proximal end cap 674 fits around drive rod 626, and isreceived in proximal end assembly 662 with the proximal end of shaft606. Proximal end assembly may include a roll gear 622 and a fluid flushentry port 664. Roll gear 622 can be made out of any stiff material,suitable materials include PEEK (glass filled and non-glass filled) andstainless steel. The flush entry port is part of roll gear 622 andmatches a luer fitting, the standard flush port used in a hospitalsetting.

As discussed above with respect to FIG. 4B, roll gear 622 forms a partof the transmission mechanism (not shown) of the surgical instrument600. Roll gear 622 is connected to a proximal end of a shaft 606 ofinstrument 600. As shown, a flush fluid entry port 664 is provided atthe proximal end of the instrument shaft. Fluid flush port 664 may bepart of the assembly that couples the outer or main body tube of shaft606 to the roll gear 622. Roll gear 622 is coupled (e.g., laser welded)to a stainless steel adaptor forming proximal end assembly 662, which isswaged over the proximal end of shaft body 624. Alternatively, roll gear622 may be coupled (e.g., laser welded or glued) directly to proximalend of shaft body 624.

As shown in FIG. 6C, a space between the multi-lumen tube 644 and theinner diameter of the shaft body 624 forms an inlet flush path 650. Asillustrated in FIGS. 6D, 6E, and 7, a fluid flush entry port 664 in anouter surface of a proximal end of a proximal end assembly of thesurgical instrument 600 provides an entry pathway for fluid into theshaft body 624 of instrument 600. As shown by the dotted line in FIG. 7,a flush fluid entering the fluid flush entry port 664 passes around andbetween multi-lumen tube 644 and inner diameter of shaft body 624 as thefluid moves from a proximal end of the instrument shaft 606 toward adistal end of the instrument shaft. As the flush fluid exits the inletflush path 650 at the distal end of multi-lumen tube 644, the flushfluid passes into space 670 between multi-lumen tube 644 and innersurface of distal end cap 666 and is redirected back into the instrumentshaft by the inner surface of distal end cap 666.

As discussed above, each of the push/pull drive rod 626 and stiffeningrods 628 passes through a respective lumen 646, 648 in multi-lumen tube644. The lumens 646, 648 have a diameter larger than that of therespective rods (drive rod 626, axial stiffening rods 628) containedtherein to allow clearance and movement between the rods and themulti-lumen tube 644. The space between the drive rod 626 and a wall ofthe central lumen 646 forms an exit flush path 652 through which fluidflows, from a distal end of the multi-lumen tube to a proximal end ofthe multi-lumen tube. Similarly, the space between each stiffening rod628 and wall of a respective lumen 648 forms an exit flush path 654through which fluid flows, from a distal end of the multi-lumen tube toa proximal end of the multi-lumen tube.

As the flush fluid exits the inlet flush path 650 at the distal end ofmulti-lumen tube 644, the flush fluid passes into space 670 betweenmulti-lumen tube 644 and inner surface of distal end cap 666 and isredirected into exit fluid flush paths 652, 654 in the multi-lumen tube644. As the fluid exits fluid flush paths 652, 654 and multi-lumen tube644, it then passes through proximal end cap 674 and exits the proximalend of instrument 600. This fluid flow path, encompassing fluid flushentry port 664, inlet fluid flow path 650, and exit fluid flow paths652, 654, provides a pathway for cleaning the shaft 606 of surgicalinstrument 600.

In accordance with the present teachings and as embodied in FIGS. 8A-8D,the instrument shaft construction disclosed herein, including shaftstiffening techniques, may be utilized with various electrosurgicaltreatment instruments. Electrosurgical instruments generally usehigh-frequency alternating current to perform a procedure on tissue ofan organism, e.g., a human patient, using heat produced by electricalenergy (e.g. cautery energy) applied to the tissue. Such instrumentsmonopolar instruments or bipolar instruments. Monopolar instrumentstypically deliver electrical energy through a single source electrode. Areturn, or sink, electrode returns electrical energy back to an energygenerator disposed externally to the patient. Bipolar instrumentstypically deliver electrical energy through two electrodes (e.g., sourceand sink electrodes), typically two jaws of the end effector of theelectrosurgical instrument, separately, and the return path for thecurrent is from one pole through the other pole. Additional informationon the structure and operation of electrosurgical instruments may befound, for example, in U.S. Patent Application Publication No.2012/0215220 A1, published Aug. 23, 2012, and U.S. Patent ApplicationPublication No. 2007/0123855, published May 31, 2007, the contents ofeach of which are incorporated herein by reference.

FIG. 8A is a perspective view of an exemplary embodiment of a distal endof a bipolar surgical instrument according to the present teachings.FIG. 8B is a perspective view of an exemplary embodiment of a proximalend of a bipolar surgical instrument according to the present teachings.FIG. 8C is a perspective view of a proximal end of a shaft portion of abipolar surgical instrument according to the present teachings. And FIG.8D is a radial cross section of the shaft of the bipolar surgicalinstrument of FIGS. 8A-8C.

As illustrated in FIGS. 8A-8D, a bipolar surgical instrument 700includes a distal end effector 704, a flexible shaft 706, and a proximalend including a force transmission mechanism 730. The bipolar distal endeffector 704 can be a scalpel, blade, hook, spatula, probe, needlepoint, dissectors, movable jaws (e.g., clamp), and any other type ofsurgical end effector equipment configured to manipulate and/orcauterize tissue and the like. The particular distal end effector 704shown in FIG. 8A is a grasper, which comprises a pair of jaws 708 and710. In this case, one of the jaws is connected to a positive electrodeand the other is connected to a negative electrode. The jaws 708 and 710can be manipulated by actuating a push/pull drive rod 726. The jaws 708and 710 are fastened together through a bolt 712 but separated by aninsulating septum 715. When the jaws 708 and 710 are open, no electricpathway exists between them. When the jaws engage a tissue or a vessel,an electric current flows from one jaw to another, passing through thetissue or the vessel, sealing or cutting it.

As shown in FIG. 8A, shaft 706 includes an outer or main body tube thatforms a shaft body 724. Shaft body 724 may include an outer skin orouter coating 734. Outer skin or coating 734 surrounds shaft body 724and reduces friction between shaft 706 and an interior of a curvedcannula as shaft 706 slides within the curved cannula. A heat shrinkmaterial such as ethylene tetrafluoroethylene (ETFE) may be used to formouter skin 734. Alternatively, other suitable materials may be used.

Within shaft body 724, a multi-lumen tube 744 provides support andalignment for a push/pull drive rod 726 of the bipolar surgicalinstrument 700. Multi-lumen tube 744 includes a central lumen 746through which push/pull drive rod 726 extends. Multi-lumen tube 744 mayinclude several lumens 748 radially spaced from central lumen 746.Multi-lumen tube 744 may be a fluorinated ethylene propylene (FEP)extrusion. FEP provides a low-friction surface against which elementswithin the lumens slide. Alternatively, other suitable materials may beused. Multi-lumen tube 744 is not anchored within shaft body 724, andmulti-lumen tube 744 is shorter in length than shaft body 724, such thatmulti-lumen tube 744 is moveable or “floats” within shaft body 724.

As illustrated in FIGS. 8A-8D, push/pull drive rod 726 extends throughthe center of multi-lumen tube 744 and is slidably moveable withincentral lumen 746 of multi-lumen tube 746. In such a “push/pull” design,pulling (tension) is used to move the component in one direction, andpushing (compression) is used to move the component in the oppositedirection. Push/pull drive rod 726 may be made from any suitablematerial, such as for example, stainless steel. Additional suitablematerials include, for example, aluminum. The push/pull drive rod 726must be made of a material and of a size sufficient to withstand thetensile and compressive forces applied during actuation of the endeffector.

As shown in FIGS. 8A-8D, one or more stiffening rods 728 are provided toincrease axial stiffness of shaft 706. The number, size, and compositionof stiffening rods 728 may be selected to provide a desired axialstiffness to shaft 706 while minimizing the impact on the bendingstiffness of shaft 706 (i.e., without increasing the bending stiffness).Like multi-lumen tube 744, stiffening rods 728 are not anchored withinshaft body 724 and are free to move or float within shaft body 724. Asdiscussed above with regard to FIGS. 6A-6E, only a single stiffeningwire contributes to the initial axial stiffness of the instrument shaft706.

As illustrated in the exemplary embodiment of FIGS. 8A-8D, fourstiffening rods 728 may be radially spaced from push/pull drive rod 726and evenly spaced from each other to surround push/pull drive rod 726.The distance the stiffening rods 728 are spaced from push/pull rod 726may be varied based on the materials used for the drive rod andstiffening rods and the dimensions of each. In some cases, increasingdistance between the push/pull drive rod 726 and stiffening rods 728 maytranslate to a slack feel, a slip, or lack of responsiveness in theinstrument. In one exemplary embodiment, the stiffening rods 728 arepositioned immediately adjacent to push/pull rod 726. As used herein,immediately adjacent includes the push/pull drive rod 726 and one ormore stiffening rods 728 being in contact or separated by only a thinsheath or other material used to position and hold the push/pull rod 726and one or more stiffening rods 728 relative to one another. Inaccordance with one exemplary embodiment, a stiffening rod 728 and adrive rod 726 positioned a distance of 0.0063 inches away from oneanother are considered to be positioned “immediately adjacent” to oneanother. Moving the stiffening rods closer to the push/pull drive rod726 and the center of the instrument shaft minimizes the differentiallength between the stiffening rods during bending of the instrumentshaft, thus transferring rod force to the end effector more effectively,and may improve responsiveness of the instrument (end effector) duringuse (e.g., provide more control over movement).

As discussed above with respect to the exemplary embodiment of FIGS.6A-6C, each stiffening rod 728 may be made of the same material aspush/pull drive rod 726, such as stainless steel 304. Alternatively, fora monopolar or a bipolar surgical instrument, it may be advantageous touse nonconductive materials for the axial stiffening rods 728 toeliminate the possibility of capacitive coupling. Capacitive couplingoccurs when energy is transferred from an electrode (conductor) throughinsulation and into other electrically isolated but conductive adjacentmaterials, such as other instruments, cannulas, or patient tissue.Although capacitive coupling is less of a risk with bipolarelectrosurgical instruments than with monopolar instruments, use ofnonconductive materials in the shaft 706 of the instrument can furtherreduce and/or eliminate this risk. Examples of suitable nonconductivematerials to be used with the stiffening rods include ceramics,zirconium, glass, fiberglass, and plastic. In addition, due to thestructure surrounding the axial stiffening rods 728, being positionedwithin multi-lumen tube 744 and being contained therein by proximal anddistal end caps, 774 and 766, it is possible to use brittlenonconductive materials for the stiffening rods 728. Should a stiffeningrod 728 made from a brittle material fracture, it will still be capableof providing axial strength to shaft 706 in the shaft structuredisclosed herein. In particular, the stiffening rod 728 can be sized tominimize the risk of fracture. Should fracture occur, the material wouldbe contained within the main tube 724, and in some cases withinmulti-lumen tube 744.

Stiffening rods 728 need not have a circular cross-sectional shape, andindeed may have any other suitable cross-sectional shapes, such as forexample, a square or triangular shape. Additionally or alternatively,each stiffening rod 728 may comprise a single rod or a plurality orbundle of rods. In an exemplary embodiment in which more than fourstiffening rods are used, a plurality of stiffening rods sufficient tosubstantially form a circle or perimeter around push/pull drive elementmay be used.

As illustrated in FIG. 8C, a conductive wire 770 extends on either sidemulti-lumen tube 744 and passes between multi-lumen tube 744 and aninner surface of shaft body 724 within passages 750 of shaft 706,through distal end cap 766, and into clevis 768, where each wire 770connects to a respective electrode of the end effector 704. Conductivewires 770 connect to a power source at a backend or transmissionmechanism (not shown) of bipolar surgical instrument 700. It should beunderstood that a shaft containing the non-conductive stiffening rodsdescribed below also may be used in a monopolar instrument. It alsoshould be understood that in some cases drive rod 726 may be directlyenergized, rather than using conductive wire(s) 770.

Further modifications and alternative embodiments will be apparent tothose of ordinary skill in the art in view of the disclosure herein. Forexample, the systems and the methods may include additional componentsor steps that were omitted from the diagrams and description for clarityof operation. Accordingly, this description is to be construed asillustrative only and is for the purpose of teaching those skilled inthe art the general manner of carrying out the present teachings. It isto be understood that the various embodiments shown and described hereinare to be taken as exemplary and elements within different embodimentsmay be used with one another. Elements and materials, and arrangementsof those elements and materials, may be substituted for thoseillustrated and described herein, parts and processes may be reversed,and certain features of the present teachings may be utilizedindependently, all as would be apparent to one skilled in the art afterhaving the benefit of the description herein. Changes may be made in theelements described herein without departing from the spirit and scope ofthe present teachings and following claims.

It is to be understood that the particular examples and embodiments setforth herein are non-limiting, and modifications to structure,dimensions, materials, and methodologies may be made without departingfrom the scope of the present teachings. Other embodiments in accordancewith the present disclosure will be apparent to those skilled in the artfrom consideration of the specification. It is intended that thespecification and examples be considered as exemplary only, with a truescope and spirit being indicated by the following claims.

What is claimed is:
 1. A method of resisting axial compression in aninstrument shaft, the method comprising: in response to application of afirst force to the instrument shaft, placing a first stiffening elementcontained within the shaft and extending between first and second endsof the shaft under a first compressive force acting along an axialdirection of the first stiffening element; and in response toapplication of a second force to the instrument shaft, subsequent to theapplication of the first force, placing a second stiffening elementcontained within the shaft and extending between the first and secondends of the instrument shaft under a second compressive force actingalong an axial direction of the second stiffening element, wherein thesecond stiffening element is not placed under an axial force in responseto application of the first force to the instrument shaft.
 2. The methodof claim 1, wherein placing the first stiffening element under the firstcompressive force occurs in response to bending the instrument shaft. 3.The method of claim 2, wherein bending the instrument shaft shortens apath between the first and second ends of the instrument shaft to placethe first stiffening element under the first compressive force.
 4. Themethod of claim 1, wherein application of the first force to theinstrument shaft is caused by initiating actuation of an end effector ofthe instrument by transmitting force through a drive rod containedwithin the shaft.
 5. The method of claim 4, wherein application of thesecond force is caused by continuing actuation of the end effector bytransmitting force through the drive rod to a full actuation of the endeffector.
 6. The method of claim 5, wherein the continuing actuationapplies the second force to the instrument shaft.
 7. The method of claim6, wherein the continuing actuation shortens a path between ends of theinstrument shaft to place at least the second stiffening element underthe second compressive force while the first stiffening element remainsunder at least the first compressive force.
 8. The method of claim 4,further comprising, in response to actuating the end effector of theinstrument with the drive rod, simultaneously placing the firststiffening element under the first compressive force and the secondstiffening element under the second compressive force.
 9. The method ofclaim 1, further comprising: during application of the first force,rotating the shaft about a longitudinal axis along the shaft; and inresponse to rotating the shaft about the longitudinal axis, unloadingthe first compressive force from being exerted on the first stiffeningelement and placing the second stiffening element under the firstcompressive force.
 10. A medical instrument comprising: a shaftcomprising a proximal end and a distal end; an end effector coupled tothe distal end of the shaft; a first stiffening element extending in theshaft, the first stiffening element having a first length; and a secondstiffening element extending in the shaft, the second stiffening elementhaving a second length; wherein the first length is sufficient for thefirst stiffening element to absorb a portion of a first axialcompression load applied to the shaft; wherein the second length issufficient for the second stiffening element to absorb a portion of asecond axial compression load applied to the shaft, the second axialcompression load being larger than the first axial compression load; andwherein the second length is insufficient for the second stiffeningelement to absorb a portion of the first axial compression load.
 11. Theshaft of claim 10, wherein on the condition that the first axialcompression load is applied to the shaft, the first stiffening elementis under compressive force between the proximal and distal ends of theshaft.
 12. The shaft of claim 10, wherein on the condition that thesecond axial compression load is applied to the shaft, the secondstiffening element is under compressive force between the proximal anddistal ends of the shaft.
 13. The shaft of claim 10, further comprising:a third stiffening element extending in the shaft, the third stiffeningelement having a third length sufficient for the third stiffeningelement to absorb a portion of a third axial compression load applied tothe shaft, the third length being insufficient for the third stiffeningelement to absorb a portion of the first and second axial loads; whereina longitudinal axis of the shaft is defined between the proximal anddistal ends of the shaft; and wherein the first, second, and thirdstiffening elements are equally spaced around the longitudinal axis ofthe shaft.
 14. The shaft of claim 10, further comprising: a thirdstiffening element extending in the shaft, the third stiffening elementhaving a third length sufficient for the third stiffening element toabsorb a portion of a third axial compression load applied to the shaft,the third length being insufficient for the third stiffening element toabsorb a portion of the first and second axial loads; and a fourthstiffening element extending in the shaft, the fourth stiffening elementhaving a fourth length sufficient for the fourth stiffening element toabsorb a portion of a fourth axial compression load applied to theshaft, the fourth length being insufficient for the fourth stiffeningelement to absorb a portion of the first, second, and third axial loads;wherein a longitudinal axis of the shaft is defined between the proximaland distal ends of the shaft; and wherein the first, second, third, andfourth stiffening elements are equally spaced around the longitudinalaxis of the shaft.
 15. The shaft of claim 10, further comprising amulti-lumen tube extending through the shaft, wherein each of the firststiffening element and the second stiffening element extend throughindividual lumens of the multi-lumen tube.
 16. The shaft of claim 15,wherein the multi-lumen tube has a first length shorter than the firstlength of the first stiffening element and shorter than the secondlength of the second stiffening element.
 17. The shaft of claim 10,wherein the first length of the first stiffening element and the secondlength of the second stiffening element are equal.
 18. The shaft ofclaim 10, wherein on the condition that the first and second axialcompression loads are not applied to the shaft, at least one of thefirst stiffening element and the second stiffening element are free tomove longitudinally within the shaft.
 19. The shaft of claim 10, whereinthe first stiffening element and the second stiffening element eachcomprise a non-conductive material.